No. I.] THE CRANIAL NERVES OF AMPHIBIA. 205 



The other longer and principal branches have been more 

 influenced and extended by the development and topographical 

 changes in various parts, such as the jaws, sense organs, etc. 

 Hatschek, however, as we have seen, does not recognize the 

 fact that there are, even of these dorsal rami, qualitatively 

 three kinds. In determining segmentation, by means of them, 

 it is necessary to decide first, whether each can represent a 

 separate segment, or all must be taken together to represent 

 one segment. The former view would rest upon the supposition 

 that some of the components for any one segmental ramus 

 have been lost. The latter view would, perhaps, seem more 

 probable, and agree better with the views here advanced as to 

 the cause of these differentiations of cutaneous nerves. 



It is questionable whether these components belong espe- 

 cially to different levels of the head and body, as Hatschek's 

 comparison with Amphioxus would seem to indicate. Each 

 one of his four sensory branches might consist, actually or 

 potentially, of the three components. From the actual rela- 

 tions in fishes, however, the general cutaneous component is 

 naturally confined to no particular locality in its innervation 

 territory. Its roots are ventral to the other two. Of the 

 other two, in origin, the lateral line component is ventral to the 

 remaining one, and is lateral in its general distribution on 

 the body. On the head there is no difference, topograph- 

 ically, in this particular respect, between the three cutaneous 

 components. 



If Hatschek's view, similar in some respects to Balfour's, is 

 correct, and the cranial nerves most closely approach the primi- 

 tive conditions, the spinal nerves having lost elements, then 

 we would naturally find these tracts, peculiar to the medulla, 

 showing the remnants, at least, of continuations in the cord. 

 Whether this were true or not, however, the validity of this 

 view would hardly be affected. 



It is useless to speculate further upon this subject. What 

 it is wished, however, to emphasize here, is the importance of 

 taking into full consideration, as a factor, the cutaneous sense 

 organs, in the attempt to obtain a philosophical understanding 

 of the changes undergone by the peripheral and central 



